Electromagnetic sound producing device



April 3, 1956 J, w TE 2,740,959

ELECTROMAGNETIC SOUND PRODUCING DEVICE Filed Nov. 17, 1954 2Sheets-Sheet l O X x 22 INVENTOR.

Joe White His Attorney April 3, 1956 J. WHITE ELECTROMAGNETIC SOUNDPRODUCING DEVICE Filed Nov. 17, 1954 2 Sheets-Sheex 2 Mun 3 3g 56 Wm so44 H 1?. 58 28 Fig. 3

f E 54 @v- V 70 INSULATION INSULATION Fig. 4

INVENTOR. Joe 65 BY His Affomey United States Patent ELECTROMAGNETICSOUND PRODUCING DEVICE Joe White, Anderson, Ind, assignor to GeneralMotors Corporation, Detroit, Mich, a corporation of Delaware ApplicationNovember 17, 1954, Serial No. 462,385

2 Claims. (Cl. 340-388) This invention relates to sound signals and moreparticularly to an improved electromagnetic assembly for use in a horn.

It is an object of the present invention to reduce contact arcing ascaused by induced currents in the electromagnet of a horn.

It is a further object to reduce the rate of fiux change in anelectromagnet of a horn so that the effect of the electromagnet on thearmature will continue after the current to the windings of theelectromagnet is interrupted.

It is another object of the present invention to eliminate theconventional arc suppressing resistances in a direct current hornassembly so as to provide a lower cost horn assembly that will operatewith higher voltages.

In carrying out the above objects it is another object of the presentinvention to include a metallic disc between a portion of the coilwindings and magnetic core of the electromagnet for a horn assembly.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Figure l is a side view of a horn embodying the present invention.

Figure 2 is a top view of the horn shown in Figure 1 with the horn coverremoved.

Figure 3 is a view, partly in section, of the horn taken along line 3--3in Figure 1.

Figure 4 is an exploded view in perspective showing the parts of themagnet assembly for a horn according to the present invention.

In the drawings the numeral designates an improved horn assembly whichmay be assembled of the parts and method described in Patent 2,677,875,filed March 11, 1949, and assigned to the assignee of the presentinvention. The horn shown in the drawings is formed with a projectorshell 22 and a backshell 24 which provides an enclosure for the powerplant of the horn. The power plant for the horn which vibrates thediaphragm 26, which is suitably secured between the projector 22 and thebase plate 28, is mounted on the base plate 28 and includes anelectromagnet assembly 30 which moves an armature assembly 32 inresponse to the opening and closing of an electric circuit as controliedby the contact assembly 34.

The armature assembly 32, shown in Figure 3, comprises a rod 36 and anarmature 38. The rod 36 extends through a bore 40 in the laminated poleassembly 42 of the electromagnet assembly 30. The armature 38 is securedto one end of the rod 36 and overlays the central portion 44 of theelectromagnet assembly 30 wherein bore 4%} is located. The end 46 of therod 36 which extends through the bore 40 is suitably secured to thediaphragm 26 so as to vibrate the diaphragm 26 when the armature 38 andthe rod 36 are moved by the electromagnet assembly 30. The end 48 of rod36 has a threaded nut adjustably located to engage and move the movablecontact 50 which is normally in engagement with the stationary contact52 of the circuit breaker assembly 34 which is fully described in thepreviously referred to patent to interrupt the flow of current to theelectromagnet assembly 30.

The contact points 50 and 52 are normally closed and connected in serieswith the coil windings 54 of the electromagnet assembly 30 and areopened mechanically as the armature 38 moves toward the pole 42 inresponse to the current flowing through the coil winding 54. When thecurrent through the coil winding 54 is interrupted by the opening ofcontacts 50 and 52, the armature returns to its original position due tothe spring-back action of the diaphragm 26. This return movement permitsthe points 50 and 52 to close and again complete the electric circuit.This action is repeated many times per second which results in a rapidvibration of the diaphragm.

The present invention is directly to an improvement in the electromagnetassembly 30 which is clearly shown in Figure 4 and comprises a laminatedpole assembly 42, a coil winding 54, a pair of formed insulating members56, an insulating disc 58 and a metallic disc 60, which will hereinafterbe described.

The laminated pole assembly 42 comprises a plurality of E-shapedlaminations of magnetic iron 62 and steel plates 63 which are suitablysecured to and form the outer layers for the laminated iron plates 62.The E-shape of the pole assembly 42 defines a pair of spaced arms 64which are integrally connected to the center portion 44. The plates 63are also provided with arms 65 whereby the assembly is secured to thebase plate 28. In the assembly of the electromagnet 30, the insulatingmembers 56, suitably formed as shown, are placed between the arms 64 ofthe E-shaped laminated magnetic pole so that the center portion 44 isembraced by a double thickness of portions 69 of the insulating paperand the U-shaped portions 70 are received between the arms 64 and centerportion 44. Before the insulating members 56 are in position, themetallic disc 60 is placed in position between the insulating members 56and the pole assembly 42. The disc 6-0 is formed of a conductive metalsuch as aluminum so as to fit between anns 64 and preferably has a shapewhich corresponds to the coil windings 54 and has a central aperture 66which surrounds the central portion 44 of the magnetic pole. The disc 60is separated from the coil windings 54 by the insulating members 56 andan insulating disc 50, which has a similar configuration to the disc 60.When the coil winding 54 is in position in the pole assembly 39 it issecurely held when flaps 68 of the insulating members 56 are bent overthe outer surface of the coil winding 54 and when tangs 70, formed onthe outer plates 63, are downwardly bent over the insulating members 56as clearly seen in Figure 3.

The conventional type of horn for 6 and 12 volts normally utilizes aresistor in parallel with contacts to limit the arcing. it has beendiscovered that the shorting washer around the flux path will reduce thearcing of the contacts almost as effectively as the resistor and at lessexpense. For voltages higher than 12 volts, the resistor across thecontacts is not sufficient, and is normally augmented with a condenserin parallel with the resistor across the contacts. The present inventionalso utilizes a condenser across the contacts in combination with ashorting washer around the flux path for horns designed to operate atvoltages above 12 volts. The effect of the shorted turn is accomplishedby the metal disc 60 in the electro-magnet assembly 3%.

The current flowing through coil winding 54 induces a field of magneticflux in the pole assembly 42. This flux attracts and causes the armature30 to move so Fat-elated Apr. 3, 1956 that the engagement betweencontacts 54. and 52 is broken. The breaking of the engagement betweenthe contacts 50 and 52 causes the current flow through the coil winding54 to be temporarily halted. When the flow of current through the coilwinding 54 ceases, field of flux around the pole assembly instantlybegins to change or decay. This decay of flux induces a potential in thecoil windings 54- which causes the contact arcing. The decay of fluxalso induces a current in the disc 6% so that it acts like a shortedturn and opposes the flux change. This opposition to the flux ch getends to sustain the flux held against its normal d y. This result isparticularly desirable in a horn electromagnet. This reduced rate offlux change at the moment the coil winding 54 circuit is opened, permitsthe magnetic effect of the pole assembly 42 on the armature to continuefor a short period after the contacts 5@ and 52 are opened and thusallows the electromagnet 39 to exert a pull while the armature assembly32 is coasting toward the end of its travel. flux decay as accomplishedby the shorted turn by sustaining the flux field also reduces the arcingat the contacts 5t) and 52 so a to make the requirement for theconventional resistance unnecessary. The above described device isparticularly uselul when horns are operated at voltages higher than theconventional 12 volts and in combination with a condenser across thecontact points, has been successfully utilized with horns of the typedescribed which operate at 36 or more volts. The utilization of ashorted turn in a horn also requires less space than the conventionalresistance so that the overall size of the horn may be reduced ifdesired without sacrifice of qualities.

While the embodiments of the present invention as herein disclosed,constitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In an electromagnetic sound producing apparatus adapted to beenergized by a direct current, the combination comprising; a magneticcore having an integral base portion, a coil winding juxtaposed adjacentthe base The lower rate of and surrounding said core and adapted toinduce a magnetic flux therein when said winding is energized, a pair ofseparable contacts adapted to interrupt the energization of saidwindings, an armature adapted to be moved by the flux of said core, adiaphragm operatively connected with said armature adapted to bevibrated in response to the movements of said armature, and a metallicdisc disposed at right angles to said core and adjacent the base of saidcore and in electrical contact therewith and insulated from said windingadapted to retard the rate of flux decay in said core and reduce thearcing between said contacts when the contacts separate.

2. In an electromagnetic sound producing device adapted to be energizedby a direct current, the combination comprising; a U-shaped magneticcore having a raised central portion extending from the base of anddisposed between the arms of said U, a coil winding positioned betweenand insulated from the arms of said core and embracing said centralportion adapted to induce a magnetic flux in said core when said windingis energized, a pair of separable contacts adapted to interrupt theenergization of said windings, a movable arrnature adapted to be movedby the flux of said core, a diaphragm operatively connected with saidarmature adapted to be vibrated in response to the movements of saidarmature, and a metallic disc disposed between the windings and the baseof said core and having a central aperture adapted to embrace andcontact the central portion of said core, and insulated from saidwinding and adapted to retard the rate of flux decay in said core andreduce the arcing between said contacts when the contacts separate.

References Cited in the file of this patent UNITED STATES PATENTS2,022,367 Carbonaro Nov. 26, 1935 2,165,582 Scofield July 11, 19392,677,875 White et a1. May 11, 1952

